Evaluating Risk Factors
and Exploration/Development Strategies
in Stratigraphic and Subtle Traps
By Jack Allan and S. Qing Sun
 Explorationists
have made a limited effort to deliberately
search for stratigraphic and subtle traps
because it is still relatively easy to
find structural traps with present-day
tools and concepts, and structural plays
are perceived as having lower risk. More
than 80% of the world's discovered stratigraphic
and subtle traps are located in the USA
and Canada. There is nothing unique about
the geology of North America to explain
this remarkable disparity, which occurs
because more wells have been drilled
there than elsewhere, and exploration
in the rest of the world has focused
largely on structural traps. This means
that a major category of oil and gas
trap has been systematically ignored
throughout most of the world.
More than 150 well-documented stratigraphic
and subtle traps, which lack obvious four-way
closure, were studied. Seven major trap categories,
which comprise sixteen individual trap types,
were defined using this data set. The major
trap categories include lateral facies change
and depositional pinchout traps, which are
created by depositional changes; unconformity
onlap/truncation and channel-/valley-fill
traps, which are related to erosion and unconformity
development; and diagenetic, fracture and
capillary-pressure traps, which have their
own unique characteristics. Trapping configuration,
closure mechanism, reservoir heterogeneity,
petroleum system, exploration and delineation
history, and geological/reservoir engineering
risks were compared and evaluated. This analysis
provided important insights into successful
exploration and development strategies and
key risk factors associated with each trap
type. |
